Site- and Orientation-Selective Anchoring of a Prototypical Molecular Building Block

Theoretical Investigation on the Initial Reaction Mechanism of Hexaethynylbenzene on Au(111) Surface

Graphyne has attracted considerable interest and attention since its successful synthesis, due to its enormous potential for applications in the fields of electronics, energy, catalysis, information technology, etc. Although various methods for synthesizing graphyne have been explored, single-layer graphynes have not been successfully developed. Hexaethynylbenzene (HEB) is considered an ideal precursor molecule because it can undergo Glaser coupling reactions between molecules to synthesize single layer graphdiyne on single crystal metal surfaces via on-surface reactions. Unfortunately, this method fails to achieve the expected results, and the underlying mechanism is not clear. In this work, we employed a combination of ab initio molecular dynamics (AIMD) and quantum mechanics (QM) methods to investigate the initial reaction mechanism of HEB molecules on a Au(111) surface. We revealed that HEB molecules undergo both intermolecular coupling and intramolecular cyclization on the Au(111) surface. The favorable pathways of these two types of reactions were then distinguished, confirming that the distance between the terminal carbon atoms of the ethynyl groups plays an important role in C-C coupling. The insights revealed from this work could facilitate the rational design of precursor molecules and deepen the understanding of the reaction processes.

Hydrogenation of Hexa-peri-hexabenzocoronene: An Entry to Nanographanes and Nanodiamonds

The fabrication of atomically precise nanographanes is a largely unexplored frontier in carbon-sp3 nanomaterials, enabling potential applications in phononics, photonics and electronics. One strategy is the hydrogenation of prototypical nanographene monolayers and multilayers under vacuum conditions. Here, we study the interaction of atomic hydrogen, generated by a hydrogen source and hydrogen plasma, with hexa-peri-hexabenzocoronene on gold using integrated time-of-flight mass spectrometry, scanning tunneling microscopy and Raman spectroscopy. Density functional tight-binding molecular dynamics is employed to rationalize the conversion to sp3 carbon atoms. The resulting hydrogenation of hexa-peri-hexabenzocoronene molecules is demonstrated computationally and experimentally, and the potential for atomically precise hexa-peri-hexabenzocoronene-derived nanodiamond fabrication is proposed.

Electronic effects and fundamental physics studied in molecular interfaces

Scanning probe instruments in conjunction with a very low temperature environment have revolutionized the ability of building, functionalizing, and analysing two dimensional interfaces in the last twenty years. In addition, the availability of fast, reliable, and increasingly sophisticated methods to simulate the structure and dynamics of these interfaces allow us to capture even very small effects at the atomic and molecular level. In this review we shall focus largely on metal surfaces and organic molecular compounds and show that building systems from the bottom up and controlling the physical properties of such systems is no longer within the realm of the desirable, but has become day to day reality in our best laboratories.

Supramolecular self-assembly of π-conjugated hydrocarbons via 2D cooperative CH/π interaction

Supramolecular self-assembly on well-defined surfaces provides access to a multitude of nanoscale architectures, including clusters of distinct symmetry and size. The driving forces underlying supramolecular structures generally involve both graphoepitaxy and weak directional nonconvalent interactions. Here we show that functionalizing a benzene molecule with an ethyne group introduces attractive interactions in a 2D geometry, which would otherwise be dominated by intermolecular repulsion. Furthermore, the attractive interactions enable supramolecular self-assembly, wherein a subtle balance between very weak CH/π bonding and molecule-surface interactions produces a well-defined "magic" dimension and chirality of supramolecular clusters. The nature of the process is corroborated by extensive scanning tunneling microscopy/spectroscopy (STM/S) measurements and ab initio calculations, which emphasize the cooperative, multicenter characters of the CH/π interaction. This work points out new possibilities for chemical functionalization of π-conjugated hydrocarbon molecules that may allow for the rational design of supramolecular clusters with a desired shape and size.

Fabrication of a well-ordered nanohole array stable at room temperature

We report on the fabrication of a new type of nanotemplate surface consisting of a hexagonally well-ordered array of one monolayer deep holes with a tunable size of about 4 nm (2) and a fixed spacing of 7 nm. The nanohole array fabrication is based on the strain-relief trigonal network formed in the 2 monolayer Ag on Pt(111) system. Removing about 0.1 ML of the Ag top layer of this surface structure, for example, by He- or Ar-ion sputtering, leads to the formation of nanoholes at specific domains of the trigonal network, which are stable at room temperature.